Balloonfish Family Diodon holocanthus
BALLOONFISH
Family - Diodontidae
Genus - Diodon
Species - holocanthus
Diodon holocanthus is known as the balloonfish and
alternatively is called the spiny puffer. These common names arise from
the predatory defense mechanisms that the species has developed. The
body is covered in long, sharp spines that stick out when the fish
inflates.
Figure 1. Typical Diodon
body spine: (A) spine (or shaft) length, (B) length of shaft
extension, (C) length of the spine base. The tip of the
spines point towards the tail.
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Figure 2. Inflated
Balloonfish (Diodon holocanthus).
Photo: © George
Burgess
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The balloonfish inflates by taking water into its body when it is
threatened. All members of the family Diodontidae are capable of
inflation. The balloonfish is distinguished from similar species by the
large, dark blotches on the side and the back that dominate its color
pattern and the small black spots interspersed between them. Unlike its
relative, the porcupinefish (Diodon hystix), these small spots do
not proliferate onto the fins. See Diodon
key
for further information.
Figure 3. A comparison between the
Porcupinefish (Diodon hystrix) left and the Balloonfish (Diodon
holocanthus) right. Note the spots on the fins of the
Porcupinefish and the dark blotches on the body of the Balloonfish.
Photos: © George Burgess
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The balloonfish is found circumtropically throughout the world's
oceans. The adults inhabit shallow water habitats and are residents of
grassy flats, mangroves, and coral reefs. They are nocturnal predators,
and generally hide in crevices during the day. The jaws are fused
together into a single unit, creating a strong, beak-like mouth capable
of cracking the shells of snails, sea urchins, and hermit crabs.
Figure 4. Worlwide
distribution of the porcupinefish (yellow) and the balloonfish
(pink).
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The balloonfish also has a pelagic, or open-ocean, life stage.
Reproduction occurs when males slowly push females to the water surface,
where they immediately spawn. The eggs are spherical, bouyant, and float
in the water. Hatching occurs roughly after four days. The larvae are
predominately yellow with scattered red spots. They are well developed
with a functional mouth, eyes, and gas bladder. Larvae less than ten
days old are covered with a thin shell.
Figure 5.
Developmental stages of the Diodon holocanthus (Balloonfish)
(A) early stage egg, (B) blastopore closure, (C) middle
stage, (D) late stage.
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Figure 6. Reared
larvae of the Diodon holocanthus (Balloonfish) (E)
newly hatched larvae 2.0mm, (F) 10-day-old larvae 2.4mm, (G)
dorsal view of 10-day-old larvae, pigment omitted.
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Figure 7. Juvenile Diodon
holocanthus (Balloonfish) displaying pelagic spotting.
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After those first ten days the shell is lost and the spines begin to
develop. The larvae undergo a metamorphosis approximately three weeks
after hatching. During this time all the fins and fin rays are present
and the teeth are formed. The red and yellow colors of the larvae do not
persist into the juvenile phase and are replaced by the olives and
browns characteristic of adults. Dark spots also appear on the
juvenile's underside. Pelagic juveniles are often associated with
floating Sargassum, and these spots may serve as camouflage from
predators such as dolphin (mahi-mahi) that swim below the seaweeds.
Juveniles retain spotting until they move inshore and become adults.
The juvenile balloonfish does not undergo another metamorphosis to
become an adult. All changes are now external and include elongation of
the spines and normal body growth. They can reach sizes up to a foot.
They are shy creatures and will retreat if approached by a diver. In
some parts of the world the dried, inflated bodies are sold as tourist
novelties.
Prepared by:
Casey Patton
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